[Lightfoot]

On my '89 LeSabre daily driver. I had to change out a caliper (RF) because the piston would not retract enough to get new pads installed.
Also the flex hose was splitting from age so I changed that at the same time.

Everything went smooth until it came time to bleed the brakes. I must have done close to a 100 pump & hold reps and it still had a few bubbles burping out every other try.
The master never came close to going dry, and everything was fine before I took the line apart at the wheel house. I gave in and bled the opposite wheel after I had run a half a quart of fluid through the repaired side. A very small bit of air spit out that (LF) side when I first tried it but it cleared out right away.
Went back to the RF and STILL getting 2-4 bb sized bubbles two out of three reps.

Finally gave up and put the wheels back on to give it a field test.
The car stops, but the stopping distance is not very impressive. And the pedal definately has a spongy feel to it when it did not beforehand.
I wouldn't feel comfortable driving over 45 on a busy road.

My lines are NOT rusty, and I have never had an issue with fluid loss.
Triple checked all the fittings are tight, I'm formally ASE certified.
And it is a new (re-man) caliper. Not salvage yard.

Any ideas?

[Lightfoot]

BTW
I drove it over 1000 miles with the new pads minus 1 inboard pad (used one old piece)
and the brakes worked fine, so it doesn't have anything to do with the friction material, et al. Rotors were turned at the time I originaly installed three out of four new pads.
I would not expect anything to be wrong with the master cylinder for this reason. It stopped OK before, but I replaced the pads because they were below 20% left.

[Chris65LeMans]

leak in the system somewhere?

[salem1912]

Two things you can check; is the caliper correct side(bleeder at the very top)? And when bleeding the system there is no need to push the m/c all the way to the floor or even pump it up. If it's an old m/c you don't want to push the m/c piston down in a area where there could be dirt or sludge,and just push the pedal 3/4 down and crack the screw. Have you tried gravity bleeding? Any play in the wheel bearing? Does the car have ABS? Sometimes you have to do some abs stops to get any air out of the Hyd unit.

[Sirrotica]

Just a guess, bottoming out the master cylinder while bleeding damaged the seals on the spool by running them over the rough part of the non used bore. Now it's sucking air into the system from the rear of the master cylinder forcing it through the system. Another reason I always gravity bleed brake systems rather than pump the brakes up and bleed them with 2 people, plus for me it's quicker, requires only 1 person.

If you remove the master cylinder from the booster there would most likely be fresh fluid on the rear of the master cylinder verifying the theory. Also less than stellar brake performance after your repair that you describe may also be an indicator of leaking seals inside the master cylinder.

I always rebuild my own calipers because the re-man quality many times leaves much to be desired. I've had more than one caliper right out of the box faulty and would rather rebuild the calipers myself than trust who knows what kind of person or attention to detail they pay their work and what is the quality of the parts they use. For re-man calipers $15-30 per side, the quality can't be that great and what was the history of, and why that core was taken off to start with.

If the master cylinder is leaking or sucking air as long as the core is rebuildable I also do my own master cylinder rebuilds. More labor intensive, but also cheaper parts wise. I trust my own work better than some strangers work.

[Lightfoot]

Brad, your theory sounds the most plausible of anything I can imagine.
I had my brother pumping and holding, and I could kind of tell he was over vigorously pumping, and pushing it all the way to the floor. But I didn't say anything, until we'd been at it for 20 minutes.

I'll unbolt the master from the booster and check for fluid back there.

It's an aluminum master cyl, so, would that be more likely to have a problem if cycled beyond the normal travel range?
Also, would installing new seals on the pistons basically revive it w/o honing the bore?

[Sirrotica]

I always hone the bores when I do them to make sure there are no protruding edges to mess up the new seals and break any glaze on the bore. Cast or aluminum makes no difference. Either is prone to corrosion from water pulled from the atmosphere by brake fluid.

[Lightfoot]

I couldn't get the master pulled away from the booster with the lines still attached.
There is evidence of fluid running down the booster in the past, and I did have a small residual dew drop of fluid clinging to the bottom rear of the master when I looked with a mirror.
Looks like I'm just going to have to R&R it.
I'm going to get a new one from Advance or NAPA. They don't seem to sell rebuild kits, and I gave my brake hones away when downsizing my tools for moving.

One question: There are two 2.5 inch hex shaped extensions between the lines and the master on the bottom 2 connecting ports. What are these, and what is their purpose?
The pictures on the parts store websites don't show them to be included with the new master cylinder.

[Lightfoot]

Here is the part I mentioned in the last post. Plus the corroded paint on the bottom of the booster. It does look like there is a miniscule bit of dampness, now that I look at the photo.

Other pictures are showing the failed attempt at compressing the piston with two large C-clamps. The 5-inch clamp got bent askew from the pressure.

[Sirrotica]

Residual pressure valves designed to keep 2 PSI in a disc brake system or 10 PSI in a drum system so there is no take up of excess clearance between pad/shoe and rotor/drum when the brakes are applied.

There is something very wrong in the system if 2 C clamps can't compress the caliper piston, 1 C clamp should be fairly easy to compress.

If it were my car I would start with cracking the connections open starting at the master cylinder and work towards the calipers to see where the restriction is. ABS systems can be a problem when dirt and corrosion is forced through them as in your situation. That will show where the restriction is as you move downstream through the system until you find the problem. You could very well have 2 problems one not allowing the calipers to compress in the form of a restriction and possible master cylinder leakage introducing air from damaged seals under negative system pressure. The restriction problem IMO, would not introduce air into the system, nor would the air introduction cause a restriction from fluid traveling back to the MC reservoir.

[Lightfoot]

The pics of the caliper were just to show how immovable the piston was in the old caliper. Taken back in July. See the first sentence in post #1.
It still functioned under hydraulic pressure to give full braking power. Just would not compress any further into the bore.

The new caliper seems to function OK.
But the pad will have a little play in it when pedal is released. I've got to double check that though. I may be thinking of when we first started bleeding and there was still a gob of air in the piston cavity.

One other thing that should be noted: I think this has a diagonal split system instead of the traditional front & rear. That's why there are four lines coming out of the master instead of two. This car does not have ABS.
If those are residual check valves, then they only serve one wheel per axle, unless I'm wrong about the diaganal braking fail safe.

[Sirrotica]

For some reason I was thinking 99 instead of 89, memory sucks when you get old. Yes diagonal braking, no ABS in 89, W/ disc drum combo. Been too long since I've worked on one of these to remember details. They may only have have the residual valves on one end of the car, you'd have to trace the lines to see. Only 1 front or 1 rear doesn't make sense.

[cuz68]

If it was that hard to press your caliper in, Makes me think it is the brake hose is not letting fluid back out.

[salem1912]

I was thinking that too but he say's in first post he replace the hose. Like Sirrotica said he going to have to crack the lines back to the m/c or m/c out to the caliper.

[necdb3]

Make sure you bleed all 4 corners also. Not sure about that model but GM used
Dual Diagonal braking systems. R/F and L/R on the same side of the master cylinder.
As mentioned before, put some wheels in the sand while braking and activate abs. sometimes air can get trapped in the abs pump.

[Lightfoot]

Yeah, its got the Diagonals. That is key to how I get this thing squared away.
Put the new master cylinder on today and having a hard time (bench) bleeding the unit. Assistant just gentley pushing the pedal with his hand.
The part came with plastic bleeder hoses for just two ports instead of four.
Trying to hold my fingers over the two open residual blocks, and it seems to keep sucking just a tiny bit of air. The forward hose cleared the air pretty normally but the rearward one just keeps pushing 6-10 bubbles out.
I finally had to give up because I was getting cold and darkness was settling in.

If I re-connect the one that is air free, can it get more air in it from the opposite two (diagonally) when they are being bled?

[salem1912]

If the new m/c came with plugs you can use them to bench bleed. Some come that way, just leave them in and push the piston in you'll see the bubbles come to the top.